The ovarian steroid hormones, estradiol and progesterone, regulate cellular functions in the central nervous system resulting in changes in physiology and reproductive behavior in a variety of species. P effects in the brain are primarily mediated through the classical genomic mechanism of action via classical intracellular progestin receptors (PRs) to modulate target gene expression. Increasing evidence suggests that P effects are also mediated via non-classical pathways to induce rapid activation of protein kinase-mediated extranuclear, intracellular signal transduction cascades. It is also becoming apparent that these rapid signaling events cross talk with the classical PR-mediated mechanisms to mediate P action. However, the receptor mechanisms mediating the rapid effects and cross talk are not well understood. We have reported P-initiated rapid activation of kinases, PKA, PKC and CaMKII in P sensitive regions of the brain. Preliminary data suggest that this rapid signaling by P activates G proteins and subsequent downstream cytoplasmic signaling molecules. We hypothesize that these rapid effects could be mediated by novel membrane receptors. The signal amplification achieved by these cascades could enhance the level of cross talk with classical PRs, facilitated by scaffolding proteins, within the neuronal cells to regulate brain and behavior. This proposal focuses on the determination of the non-classical mechanisms of P action that extend beyond the classical intracellular steroid receptor- mediated pathways. In particular, we propose to determine the biochemical and molecular events underlying the rapid P- activated signaling pathway(s) in P-sensitive areas of the rat brain. Specific aim 1 will identify the mechanism underlying the rapid P activation of G proteins and the downstream signaling pathways in vitro. Specific aim 2 will examine the in vivo functional relevance of G protein-mediated mechanisms in P- mediated signaling and behavior. Specific aim 3 will test the hypothesis that a scaffolding protein integrates the rapid extranuclear signaling pathways with the intracellular PR-mediated genomic pathway in brain and behavior.